Palaeoearthquakes on the Kelkit Valley Segment of the North Anatolian Fault, Turkey

Turkish Journal of Earth Sciences (Turkish J. Earth Sci.), Vol.C. ZABCI20, 2011, ET pp. AL. 411–427. Copyright ©TÜBİTAK doi:10.3906/yer-0910-48 First published online 14 June 2010 Palaeoearthquakes on the Kelkit Valley Segment of the North Anatolian Fault, Turkey: Implications for the Surface Rupture of the Historical 17 August 1668 Anatolian Earthquake CENGİZ ZABCI1,*, HÜSNÜ SERDAR AKYÜZ1, VOLKAN KARABACAK2, TAYLAN SANÇAR3,4, ERHAN ALTUNEL2, HALİL GÜRSOY5 & ORHAN TATAR5 1 İstanbul Teknik Üniversitesi, Ayazağa Yerleşkesi, Jeoloji Mühendisliği Bölümü, Maslak, TR−34469 İstanbul, Turkey (E-mail: [email protected]) 2 Eskişehir Osmangazi Üniversitesi, Jeoloji Mühendisliği Bölümü, TR−26040 Eskişehir, Turkey 3 İstanbul Teknik Üniversitesi, Ayazağa Yerleşkesi, Avrasya Yerbilimleri Enstitüsü, Maslak, TR−34469 İstanbul, Turkey 4 Tunceli Üniversitesi, Mühendislik Fakültesi, Jeoloji Mühendisliği Bölümü, TR−62000 Tunceli, Turkey 5 Cumhuriyet Üniversitesi, Jeoloji Mühendisliği Bölümü, TR−58140 Sivas, Turkey Received 02 November 2009; revised typescript receipts 20 May 2010; accepted 14 June 2010 Abstract: Th e 26 December 1939 Erzincan (Ms= 7.8) and 20 December 1942 Erbaa-Niksar (Ms= 7.1) earthquakes created a total surface rupture more than 400 km between Erzincan and Erbaa on the middle to eastern sections of the North Anatolian Fault. Th ese two faulting events are separated by a 10-km-wide releasing stepover, which acted like a seismic barrier in the 20th century. To understand the rupture behaviour in this structurally complex section of the North Anatolian Fault, we undertook palaeoseismological trench investigations on the Kelkit Valley segment where there is little or no palaeoseismic information. We found evidence for three surface faulting earthquakes predating the 1939 event during the past millennium in trenches excavated in Reşadiye and Umurca. In addition to the 1939 Erzincan earthquake, prior surface ruptures are attributed to the 17 August 1668, A.D. 1254 and A.D. 1045 events. Surface rupture of the 17 August 1668 Anatolian earthquake was previously reported in palaeoseismological studies, performed on the 1944, 1943, and 1942 earthquake fault segments. We suggest that the surface rupture of this catastrophic event jumped the 10-km-wide releasing stepover in Niksar and continued eastward to near Koyulhisar. Th e existence of diff erent amount of off sets in fi eld boundaries (sets of 4 m, 6.5 m, and 10.8 m) was interpreted as the result of multiple events, in which the 1939, 1668, and 1254 surface ruptures have about 4, 2.5, and 4 metres of horizontal coseismic slip on the Kelkit Valley segment of the North Anatolian Fault, respectively. Key Words: North Anatolian Fault, palaeoseismicity, earthquakes, Kelkit Valley, Turkey, 1668 Anatolian earthquake Kuzey Anadolu Fayı, Kelkit Vadisi Segmenti’nin Eski Depremleri: Tarihsel 17 Ağustos 1668 Anadolu Depreminin Yüzey Kırığı ile İlgili Bulgular Özet: Kuzey Anadolu Fayı’nın orta ve doğu kesimlerinde gerçekleşen 26 Aralık 1939 Erzincan (Ms= 7.8) ve 20 Aralık 1942 Erbaa-Niksar (Ms= 7.1) depremleri, Erzincan ve Erbaa arasında toplam 400 km’den daha uzun bir yüzey kırığı yaratmıştır. Bu iki faylanma olayı, 20. yüzyılda sismik bir bariyer işlevi görmüş olan 10 km genişliğindeki açılmalı bir sıçrama ile birbirlerinden ayrılır. Kuzey Anadolu Fayı’nın yapısal olarak karmaşık bu kısımının sahip olduğu kırılma davranışının daha iyi anlaşılması için Kelkit Vadisi segmenti üzerinde paleosismolojik hendek çalışmaları gerçekleştirilmiştir. Reşadiye ve Umurca’da açılan iki hendek sonucu son bin yıl içerisinde gerçekleşmiş 1939 Erzincan depremine ek olarak toplam üç olay tespit edilmiştir. Bunlar, sırasıyla 17 Ağustos 1668, M.S. 1254 ve M.S. 1045 tarihsel depremleri ile deneştirilmişlerdir. 17 Ağustos 1668 Anadolu depremine ait yüzey kırığı, 1942, 1943 ve 1944 deprem fay segmentlerinin üzerinde daha önceden gerçekleştirilen birçok paleosismoloji çalışmasında belirlenmiştir. Bu büyük deprem, Kelkit Vadisi segmenti üzerinde açılan hendeklerin sonuçlarına göre, Niksar’da yer alan 10 km genişlikteki açılmalı sıçramayı aşmış ve Koyulhisar yakınlarına kadar uzanan bir alana kadar kırılmıştır. Ayrıca, tarla sınırları üzerinde ölçülen farklı ötelenme miktarlarının (4, 6.5 ve 10.8 m) varlığı, birden fazla depremin etkisi olarak yorumlanmıştır. Buna göre Kuzey Anadolu Fayı, Kelkit Vadisi segmenti üzerinde, yaklaşık 4 m’lik atım 1939 Erzincan, 2.5 m’lik atım 1668, 4 m’lik atım 1254 depremleri sonucunda gerçekleşmiş olmalıdır. Anahtar Sözcükler: Kuzey Anadolu Fayı, paleosismisite, depremler, Kelkit Vadisi, Türkiye, 1668 Anadolu depremi 411 PALAEOEARTHQUAKES ON THE KELKIT VALLEY SEGMENT OF THE NAFZ Introduction 1939 and 1999, in a westward-migrating sequence, Th e North Anatolian Fault (NAF) is one of the world’s along a 1000-km-long zone of continuous surface most important active dextral strike-slip structures, ruptures (Blumenthal 1945; Ambraseys & Zatopek extending more than 1500 km from eastern Turkey 1969; Ketin 1969; Barka 1996, 1999; Akyüz et al. to the northern Aegean Sea (Figure 1a). Th is 2002; Barka et al. 2002; Kondo et al. 2005; Pucci et deformation zone is the northern boundary of the al. 2006). westward moving Anatolian block and connects the Th e 26 December 1939 Erzincan (Ms= 7.8) and 20 Aegean extensional regime with East Anatolian high December 1942 Erbaa-Niksar (Ms= 7.1) earthquakes plateau (Ketin 1948; Şengör 1979; Barka & Kadinsky- created a total surface rupture more than 400 km Cade 1988; Barka 1992; Şengör et al. 2005). Eight between Erzincan and Erbaa (Figure 1b) (Ketin large earthquakes occurred along the NAFZ between 1969; Barka 1996; Ambraseys & Jackson 1998). As 36˚ 37˚ 38˚ 39˚ 28˚ 32˚ 36˚ 40˚ 44˚ 42˚ 42˚ 42˚ 42˚ Anatolian Fault The North 40˚1 2 3 40˚ FigureFigure 1b1b 38˚ 38˚ East Anatolian Fault 36˚a 36˚ 28˚ 32˚ 36˚ 40˚ 44˚ 41˚ 4 41˚ 5 Giresun 6 Erbaa Niksar Amasya 7 10-km-wide step-over Reşadiye Köklüce Koyulhisar Tokat FigureFigure 2 Suşehri Kelkit Valley Segment 40˚ 8 40˚ Refahiye 1939, 1942, 1943, N Erzincan Erbaa-Niksar Tosya Erzincan surface surface surface rupture rupture rupture 0 25 50 km b 36˚ 37˚ 38˚ 39˚ Figure 1. (a) Map of the North Anatolian Fault and other active faults in Turkey (Şaroğlu et al. 1992). Numbers indicate palaeoseismic trench sites, 1– Okumura et al. (2003) & Kondo et al. (2004, 2010), 2– Sugai et al. (1999), 3– Yoshioka et al. (2000). White lines show the location and probable extent of faulting associated with the earthquake of 1668. (b) Simplifi ed map shows traces of 1939, 1942 and partly 1943 earthquake ruptures (drawn from Ketin 1969 and Barka 1996). Th e 10-km-wide releasing stepover is clearly visible between 1939 and 1942 ruptures, extending between Niksar and Köklüce. Numbered circles are locations of previous trenches performed by 4– Hartleb et al. (2003), 5– Fraser et al. (2009), 6– Kurçer et al. (2009), 7– Kondo et al. (2009) and 8– Hartleb et al. (2006). 412 C. ZABCI ET AL. Figure 1b shows, these two earthquake segments are earthquake is not reported in the Havza trenches separated by a 10-km-wide releasing stepover, near (site 3 in Figure 1a) (Yoshioka et al. 2000). Signs of Köklüce, at the eastern boundary of the Niksar Basin the 1668 historical event are documented by Kurçer (Barka & Kadinsky-Cade 1988; Barka et al. 2000). et al. (2009) (site 6 in Figure 1b) and Kondo et al. Th is geometric discontinuity of the fault zone acts (2009) (site 7 in Figure 1b) on the most western and as a seismic barrier, stopping rupture propagation or eastern sections of the 1942 Erbaa-Niksar rupture changing its direction in the 1939 and 1942 ruptures as the most eastern evidence for faulting during the (Wesnousky 1988). In contrast, the historical 1668 event. Although palaeoseismic evidence exists Anatolian Earthquake of 17 August 1668, thought for the rupture of the 1668 earthquake on 1942, 1943 to have a probable rupture length of more than 400 and 1944 ruptures, there are no signs of a historical km, starts from east of Gerede, crossing the 10-km- earthquake between the 14th and 19th century on the wide releasing stepover in Niksar, and terminates 1939 Erzincan earthquake surface rupture. At the near Koyulhisar (Figure 1a) (Ambraseys & Finkel Çukurçimen site (site 8 in Figure 1b) evidence for 1988). However, some other historical earthquake faulting prior to the 1939 event has an upper age catalogues (e.g., Pınar & Lahn 1952; Ergin et al. 1967) limit of A.D. 1420 and is interpreted to be the A.D. suggest that instead of one large earthquake, a series of 1254 historical earthquake (Hartleb et al. 2006). Th is events occurred between July and September 1668 in information suggests that surface rupture of the 1668 various places (Pınar & Lahn 1952; Ergin et al. 1967). earthquake did not extent further east than Refahiye. Because of ambiguity in the historical information, In the light of the above discussion, the main the spatial distribution of the 1668 rupture and objective of this study is to provide more constraints recurrence of large prior earthquakes in this region to evaluate the 17 August 1668 Anatolian earthquake can only be derived from palaeoseismology. Several rupture distribution. It is very important to palaeoseismological investigations were carried out understand the following questions; does a releasing in the west of the 10-km-wide releasing stepover stepover, with a width of 10 km, act as a seismic-barrier (Figure 1b) (Sugai et al. 1999; Yoshioka et al. 2000; like it did on 1939 and 1942 earthquakes, or can it be Hartleb et al. 2003; Okumura et al. 2003; Kondo et crossed by a surface rupture produced by the release al. 2004, 2009; Fraser et al. 2009; Kurçer et al. 2009). of very high seismic energy? Any evidence about the Th e Ardıçlı trench site (located 9 km east of Gerede) rupture process on this complex fault geometry will and the Demirtepe trench site (located 12 km east of give us a better understanding for the construction of Gerede) expose the penultimate event in A.D.

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